The present invention relates to a method of forming a nozzle for an ejection device for ejecting or spraying a liquid or a gas. More particularly, the present invention relates to a method of forming a nozzle having a cross-section which is made smaller stepwise toward the front end thereof by etching a silicon monocrystalline substrate. Further more, the present invention relates to a method of forming a nozzle plate which is preferable for an inkjet head for ejecting ink droplets.
For example, the inkjet head of an inkjet printer generally comprises a plurality of nozzles for ejecting ink droplets therefrom and an ink supply passage communicating with the nozzles.
Recently, it has become necessary to more precisely and more minutely process inkjet heads to permit ultrafine characters to be printed. For this purpose, there have been proposed many methods of forming micropore nozzles by applying anisotropic-etching to a silicon substrate.
It is preferable to use a nozzle having such a cross-sectional shape that a thin nozzle hole portion is formed on the front end side thereof and a nozzle hole portion expanding in a conical shape or a pyramidal shape is formed at the rear end side thereof in order to improve the ink ejection characteristics of the respective nozzles of an inkjet head. For example, as disclosed in Japanese Unexamined Patent Publication No. 56-135075, when a nozzle is formed in a cylindrical shape at the front end side thereof and the inner periphery of the nozzle is formed in a truncated-quadrangular-prism shape at the rear side thereof, the directions of ink pressures imposed on nozzles from an ink cavity side can be aligned in the axial directions of the nozzles, as compared with a case where cylindrical nozzles are used. Stable ink ejection characteristics can be obtained thereby. That is, since variations in the trajectories of ink droplets can be eliminated, they are prevented from flying in differing directions, whereby variations in the amount of the ink droplets can be suppressed.
As disclosed in Japanese Unexamined Patent Publication No. 56-135075, however, since the truncated-quadrangular-prism-shaped inner periphery of the nozzle on the rear side is formed in a silicon substrate using anisotropic-etching, the inner periphery is formed along the crystal direction of the silicon. Thus, the angle of the inclined rear portion of the nozzle is reduced to obtain an action for aligning the directions of ink pressures imposed on the nozzles from the ink cavity side in the axial directions of the nozzles. That is, it is impossible to decrease the cross-sectional area of the nozzle on the rear side thereof.
In contrast, for example, Japanese Unexamined Patent Publication No. 5-50601, filed by the applicants, discloses a method of manufacturing an electrostatic drive type inkjet head in which a nozzle and an ink supply passage are formed with pinpoint accuracy by applying photolithography and wet-type-crystal-anisotropic etching to a silicon monocrystalline substrate.
The inkjet head disclosed in the publication employs a structure in which nozzles, reservoirs, ink supply passages such as cavities and the like, and diaphragms are formed on a silicon monocrystalline substrate bonded to a glass electrode substrate, on which electrodes for deflecting the diaphragms by electrostatic force are formed.
The use of this structure allows a manufacturing method to be employed in which after the patterns (nozzles, ink supply passages, electrodes) of respective inkjet heads are formed on the respective substrates, the substrates are bonded to each other and the thus-bonded substrates are cut and separated into the respective inkjet heads (the so-called method of making multiple inkjet heads from a single substrate), whereby the inkjet heads can be manufactured at low cost. Note that an example of the method of making multiple inkjet heads from a single substrate is disclosed in Japanese Unexamined Patent Publication No. 9-300630, filed by the applicants. Specifically, the publication proposes a method of bonding a plurality of cover substrates and a flow passage substrate in a row state so that terminals formed at a lower substrate to supply a signal or power are exposed.
Incidentally, when nozzles are formed on a cover substrate for covering an ink supply passage and the cover substrate itself is used as a nozzle plate, it is preferable for accuracy that after a single nozzle plate is bonded to a flow passage substrate, the combined substrate be separated to respective inkjet heads, as compared with the method disclosed in Japanese Unexamined Patent Publication No. 9-300630.
In this case, a through-hole for exposing terminals formed on the lower substrate must be formed, in addition to the nozzles, on the nozzle plate as the uppermost substrate of these three substrates.
Etching is carried out at a relatively low rate in a process for forming nozzle holes because pinpoint processing accuracy is required in the process. In contrast, etching is carried out at a relatively high rate in a process for forming the through-hole whose accuracy is relatively not as stringent as that for the nozzle holes because a reduction in etching time takes precedence over processing accuracy. As a result, the process for forming the nozzle holes and the process for forming the through-hole, the etching conditions of which are different from each other, have ordinarily been performed independently from each other. That is, after the through-hole is formed by etching, the nozzle holes are etched; or after the nozzle holes are formed by etching, the through-hole etched.
Thus, all the sub-processes relating to the etching process, such as patterning including the formation of a resist film, masking, and the removal of the resist film, rinsing, and the like, must be carried out twice, whereby problems arise in that the manufacturing process is complex and the manufacture is time-consuming.
Problems to be solved by the present invention, which was made in view of the above points, primarily reside in the following two points:
1) to propose a method for forming a nozzle for an ejection device in a monocrystalline silicon substrate, the nozzle having a substantial action for aligning the directions of pressures imposed on nozzles from a cavity side in the axial directions of the nozzles, as compared with the action obtained by a conventional method; and
2) to propose a method for manufacturing an inkjet head capable of forming a nozzle without lowering the processing accuracy thereof, as well as capable of forming a through-hole, which is very large relative to the nozzle, on a monocrystalline silicon substrate simultaneously with the formation of the nozzle, thereby simplifying the manufacturing process and reducing manufacturing time.
To solve the problem 1), the present invention employs a dry-etching method by ICP (induction coupled plasma) discharge as an anisotropic dry-etching method to form a nozzle having a cross-section made smaller stepwise toward the front end thereof by applying etching to a silicon monocrystalline substrate.
That is, in a method of forming a nozzle of the present invention, first, an oxidized silicon film, for example, is formed as a resist film on a surface of the silicon monocrystalline substrate. Next, a first opening pattern is formed by removing the resist film at a portion corresponding to the rear end of the nozzle and a second opening pattern which is smaller than the first pattern is formed by removing the resist film at a portion corresponding to the front end of the nozzle. Next, dry-etching is applied by plasma discharge to the exposed portions of the surface of the silicon monocrystalline substrate exposed by the first and second opening patterns. At this time, a gas for etching silicon by conversion to a plasma by plasma discharge and a gas for suppressing the etching of silicon by conversion to a plasma by plasma discharge are alternately charged into a processing vessel in which the silicon substrate is disposed. With this processing, a nozzle is formed having a cross-section which coincides with the shapes of the respective opening patterns and is made smaller stepwise from the rear end thereof toward the front end thereof.
Furthermore, when the respective opening patterns are formed as described below, a nozzle whose cross-section is made smaller stepwise from the rear end thereof toward the front end thereof can be formed by performing dry-etching only from one side of the silicon substrate, whereby the manufacturing process can be further simplified.
That is, after a resist film is formed on a surface of the silicon monocrystalline substrate, the opening pattern, which corresponds to the portion of the nozzle at the rear end thereof, is formed at the resist film by half-etching the resist film (first patterning process). Next, an opening pattern which corresponds to the portion of the nozzle at the front end thereof is formed as the exposed portion of the surface of the silicon monocrystalline substrate by full-etching a portion of the half-etched region of the resist film at which the above opening pattern is formed (second patterning process). Thereafter, a first groove having a predetermined depth is formed by applying dry-etching to the exposed portion of the silicon monocrystalline substrate by plasma discharge (first dry-etching process). Then, after the surface of the silicon monocrystalline substrate is exposed by full-etching the half-etched region of the resist film, a second groove having a predetermined depth, while the first groove remains on the bottom thereof, is formed by applying dry-etching to the silicon monocrystalline substrate by plasma discharge (second dry-etching process).
When anisotropic-dry-etching is started by plasma discharge in the first dry-etching process, only the surface portion of the silicon monocrystalline substrate whose surface is exposed by the full-etching is vertically removed by the etching so that the first groove having a predetermined depth is formed. In the second dry-etching process, the etching of the surface of the silicon monocrystalline substrate is conducted in a state in which the first groove which was formed first by the etching remains as it is, and the second groove is formed. When etching conditions are properly determined, the depth of the portion of the first groove can be set to a size which coincides with the nozzle at the front end thereof having a small cross-section and the depth of the portion of the second groove can be set to a size which coincides with the nozzle at the rear end thereof having a large cross-section.
According to the method, a master pattern need not be repeatedly formed on the surface of the silicon monocrystalline substrate. Further more, a master pattern need not be formed along the surface of the silicon monocrystalline substrate in the stepwise state after a recess is formed at the silicon monocrystalline substrate. Thus, according to the nozzle forming method of the present invention, the nozzle having the stepwise-cross-section can be effectively and simply formed.
To solve the problem 2), the present invention employs a method arranged such that a first fine groove acting as the nozzle is formed up to a predetermined depth and a second groove acting as a part of a through-hole, which exposes a terminal disposed on a substrate to be bonded to the lower side of a substrate serving as a nozzle plate, are formed from a surface of the substrate serving as the nozzle plate by etching. Thereafter, a third groove, larger than the first groove, is formed from the other surface of the upper substrate by etching, and the nozzle and the through-hole are simultaneously formed by penetrating the first groove and the second groove.
With this procedure, the through-hole can be formed simultaneously with the nozzle without lowering processing accuracy. When the through-hole is relatively large, it is preferable to form the second groove by etching into a shape which follows the contour of the outer periphery of the through-hole. Since the etching area of the portion of the through-hole can be reduced thereby, the reduction of etching speed can be prevented, and the deterioration of the accuracy of the grooves in a depth direction caused by the etching applied to a wafer surface can be prevented.